An economist claims, based on an econometric study, that high profits in a certain industry are explained by that industry's high Herfindahl-...

An economist claims, based on an econometric study, that high profits in a certain industry are explained by that industry's high Herfindahl- Hirschman Index (HHI). If you felt, based on your knowledge of the industry that this claim were untrue, what critical questions could you ask about the HHI used for the study?